There are several types of spun yarns commonly used in the construction of woven fabrics. Among the most common, and familiar to those versed in the art, are ring spun, open-end spun (OES), air-jet spun (AJS), and roller jet spun (RJS) yarns. Ring spun yarns consist of generally helically wound fibers which, when woven into fabrics, exhibit excellent hand and strength characteristics. It is known that, as the twist level is increased for ring spun yarns, the fabric containing them becomes stiffer and harsher, as increased twist reduces fiber-to-fiber mobility. OE yarns, compared to ring spun yarns, are more disorganized and have a lower twist. The fiber bundle comprising the yarn is compacted by the presence of tightly wound wrapper fibers, which are nearly perpendicular to the axis of the yarn. As the yarn structure of OE yarns is less organized than that of ring spun yarns, the OE yarn exhibits a larger diameter than that of a ring spun of an equivalent denier. The larger size of the OE yarn, coupled with the lack of mobility of the fibers, because of the pressure imparted by the wrapper fibers, results in a stiffer fabric, in spite of the lower twist as compared to ring spun yarns. The tightly wound wrapper fibers also cause the surface of the fabric to be harsh and scratchy to the touch. The relative fiber immobility makes it difficult to enhance the fabric by needling with hydraulic jets, as these yarns cannot easily blossom when constricted by the wrapper fibers. In the same way, wrapper fibers reduce the effectiveness of pneumatic vibratory softening as disclosed in my U.S. Pat. No. 4,918,795, entirely incorporated herein by reference. As the wrapper fibers are not aligned with the axis of the yarn, they do not contribute to fabric strength, and fabrics constructed of yarns containing wrapper fibers are generally not as strong as fabrics constructed of ring spun yarns. AJS and RJS yarns are similar to OE yarns, but have core fibers with little or no twist, and the integrity of the yarn entirely depends upon the presence of the wrapper fibers. Without the fiber-to-fiber friction created by the pressure exerted by the wrapper fibers, the yarn would have no tenacity and could not be woven into fabrics. Once a fabric has been woven, yarn-to-yarn pressures are sufficient to create frictional forces between fibers, and the wrapper fibers are no longer necessary for strength. Loosening or cutting wrapper fibers, by various means such as by sanding or napping, so as to improve the hand and other properties, without substantial cutting of the load bearing fibers, can dramatically improve the hand and surface touch of the fabric, allow the fabric to blossom when hydraulically needled or to soften when pneumatically vibrated, as well as improve adhesion to coatings, without degrading fabric strength. Other methods of sanding and abrading textile fabrics are known, such as that disclosed in U.S. Pat. No. 5,058,329, to Love et al., entirely incorporated herein by reference, however they are not effective in severing or sufficiently loosening the wrapper fibers within the fabric in order to create significant associated benefits resulting therefrom without also cutting load bearing fibers and substantially reducing the strength of the fabric.
While it is possible to cut the non-load bearing wrapper fibers in the yarns without substantially reducing the fabric tensile properties, as is disclosed in my U.S. Pat. applications 08/738,787 and 08/995,184, both entirely incorporated herein by reference, it is often desirable to achieve a sueded finish by means of various types of surface abrasion, wherein load bearing fibers are also cut. However, several problems may result from such a process.
One problem associated with such surface abrasion of textile webs is the possibility of producing streaks within the resultant fabric. These are relatively lighter or darker lines that appear in the warp direction. While these may be due to fabric or yarn irregularities, they may also occur due to random variation in the grit particles. If a particularly large or aggressive particle is present, more fibers will be cut, and lighter colored fibers in the yarn core may be exposed, producing a streak. One method of mollifying the effect of individual grit particles is to make the abrasive drum very large so that the effect of a single grit particle is not continuous. However this method reduces the pressure of the fabric against the treatment roll, requiring either relatively coarse grit, or some other means to create pressure, such as through the utilization of flaps, backup rolls, or air pressure. Another method is to make the streak more difficult to observe by oscillating the treatment rolls along the rotational axis, creating a sinusoidal pattern on the fabric, so that the effect of single grit particles spread out. Oscillation is often used in multi-roll treatment machines, with the oscillations timed so as not to be superimposed.
Another common problem with all abrasive processes is that the cutting of fibers reduces the tensile properties of the fabric, regardless of yarn type. Also, except in the case of warp-faced fabrics, there is more interaction of the abrasive particles with the fibers of the fill yarns, since these fibers are more perpendicular to the movement of the abrasive particles as compared to the fibers of the warp yarns. This interaction results in relatively greater abrasion and strength degradation to the fill yarns, and may result in the shifting of fill yarns relative to warp yarns in the fabric. Compounding this problem is that, for reasons of weaving economy, many fabrics are more lightly constructed in the fill direction and therefore are initially weaker in that direction. Fibers of warp yarns, in particular filament yarns, are more difficult to cut where there is a parallel orientation of the abrasive particles and the filaments. Thus, a method of abrasively treating a web so as to retain fill strength while also avoiding a streaky appearance is needed. The present invention solves these problems in a manner not disclosed in the known prior art while producing a textile potentially having fewer noticeable defects than by other heretofore employed methods.